BTS (Korean: 방탄소년단; RR: Bangtan Sonyeondan), also known as the Bangtan Boys, is a seven-member South Korean boy band formed in Seoul in 2013. The septet co-writes and produces much of their output. Originally a hip hop group, their musical style has evolved to include a wide range of genres. Their lyrics, often focused on personal and social commentary, touch on the themes of mental health, troubles of school-age youth, loss, the journey towards loving oneself, and individualism. Their work features references to literature and psychological concepts and includes an alternative universe storyline. The group have staged several world tours.